Access point for managing wireless access to a network according to a zone of operation about the access point

ABSTRACT

A method of managing wireless access to a network performed by an access point includes storing a programmable response time for defining a zone of operation around the access point, receiving from a client device a request to associate with the access point, transmitting a probe to the client device, when a response to the probe is received, measuring a round trip time between transmission of the probe and receipt of the response, determining whether the client device&#39;s request to associate with the access point should be granted or denied by comparing the round trip time to the programmable response time, granting the request to associate in response to determining that the round trip time is less than the programmable response time, and denying the request to associate with the access point in response to determining that the round trip time is longer than the programmable response time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/505,577 filed Oct. 3, 2014; which is a continuation of U.S. patentapplication Ser. No. 13/013,659 filed Jan. 25, 2011; which is a divisionof U.S. patent application Ser. No. 11/534,190 filed Sep. 21, 2006;which claims the benefit of priority of U.S. Provisional PatentApplication No. 60/813,993 filed on Jun. 14, 2006. All of the abovereferenced applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present invention relates to wireless networks and, in particular,to a variety of techniques for the deployment and operation of accesspoints in wireless networks to improve capacity and geographicisolation.

(2) Description of the Related Art

Wireless networks typically employ egress/access devices, commonlyreferred to as access points, which form points of presence for clientradio devices. An access point may act alone in its function but isoften deployed in an array or cellular structure with predictable andoverlapping coverage from cell to cell. Client devices act as end-pointsfor telemetry and data transferred to and from access points, or asprocessing points for the telemetry. In a conventional wireless networkhaving multiple access points, a client device will typically associatewith the access point for which it experiences the most favorablesignal-to-noise ratio (SNR). The client will then attempt to remainassociated with that access point for as long as possible (e.g., bytuning down the data transfer rate).

To avoid interference between adjacent access points, conventionalwireless networks often employ different channels within the RF band ofinterest for different access points, e.g., channels 1, 6, and 11 in theRF band associated with IEEE 802.11, the set of standards relating towireless local area networks. Careful control of the signal intensitiesfor adjacent access points is also used to reduce the likelihood thatthe access points will interfere with each other.

In a wireless network based on IEEE 802.11 or similar technologies, itis desirable that client devices be able to roam seamlessly from oneaccess point to another. In some applications, it is also desirable toprovide and support a variety of functionalities including, for example,independent data paths, multiple data types, independent userpermissions, and independent security protocols allowing or restrictingaccess or content based on geographic or venue locations within anenvironment which may offer little restriction to radio frequencypropagation. For example, it may be desirable to enable a user at avenue with the proper permissions to roam from a public area such as ahallway or lobby into a meeting room or convention area. In these newareas the user would then have access to data and permissions notallowed or available in the public area. The capability of restrictingthe area of influence or usability by defining strict geographicboundaries, i.e., geographic isolation, enhances or enables a widevariety of services such as, for example, E-911, Point location (i.e., a“You Are Here” service), billing by location, traffic management, datasecurity, access control, etc.

Geographic isolation may be conventionally achieved by restricting thebroadcast power of the transmitting access point or base station, and insome circumstances the transmitting power of the client devices. In someapplications the Effective Isotropic Radiated Power (EIRP) of both theaccess point and client device may be restricted. This approach ishighly effective in large open areas but breaks down in confined areassuch as inside buildings or dense urban environments in which “canyoneffects” tend to deduct signal.

In some applications, the attenuation presented by structures in theenvironment may not present a substantial barrier to signal propagation.This may be especially true, for example, in conference or officeenvironments that may only be separated by glass, or thin, movablepartitions. It is often not technically feasible to “dial down” thepower of a transceiver to the point where it would continue to be usefulin its intended area without transmitting beyond such barriers. Inaddition, reducing the transmission power of access points increasesareas of shadow (or signal detected from other access points), whiledecreasing the ratio of signal to noise. These are both undesirableresults in that they increase the likelihood that a client device mightroam to an out-of-area access point. And even where this technique maybe used successfully, it can be easily defeated by the use of relativelyhi-gain antennas on client devices that enable reaching far beyond theintended area of geographic isolation.

Accurate determination of the location of client devices may also beused to achieve the goals associated with geographic isolation. That is,if the position of a client device is known within an environment,access to services may be controlled on that basis. Presently, wirelesssystems and devices rely on averaged signal strength from a known sourcepoint for location telemetry. The accuracy of the location can beimproved upon, by a process known as triangulation. Triangulation is aprocess by which the location of a radio transmitter can be determinedby measuring either the radial distance, or the direction, of thereceived signal from three different points. For example, the distanceto a cell phone may be determined by measuring the relative time delaysof the normal communications signal from the phone to three differentbase stations. Signal strength measurements in combination withtriangulation have proven to be quite accurate in open environments.However, closed environments such as building interiors and dense urbanareas present conditions which seriously degrade the efficacy of suchtechniques.

That is, the combination of reflection, refraction, multi-path, andsignal absorption in such environments form complex boundary conditionsmaking position predictions based on signal strength and triangulationtricky and often inaccurate. Methods to correct for these effectsinvolve highly complex modeling and mapping of signal levels in theenvironment. And unfortunately, this time consuming and expensive“correction” falls apart if even a small change occurs from the baselinemapping. These small changes include thing like a door opening orclosing, a curtain being opened exposing a reflective pane of glass, oreven something as innocuous as the variable flow of water in plumbing.

Another conventional approach to determining the location of clientdevices is accomplished using global positioning systems (GPS)technologies. Unfortunately, such technologies are not always reliableinside buildings or in dense urban environments in that the reach of GPSequipment is limited by the attenuation caused by surroundingstructures. GPS solutions also involve the use of secondary equipment,increasing system costs and introducing an additional point of failure.

In view of the foregoing, it is desirable to provide improved techniquesfor deploying wireless access points, base stations and the like.

BRIEF SUMMARY OF THE INVENTION

According to a specific embodiment of the present invention a wirelessnetwork is provided which includes a plurality of access devices forenabling wireless access to the network by a plurality of clientdevices. A first one of the access devices is configured to inhibitassociation of the client devices with the first access device at datarates below a predetermined data rate, thereby creating a zone ofoperation outside of which the client devices are unlikely to associatewith the first access device.

According to another specific embodiment, a wireless network is providedwhich includes a plurality of access devices for enabling wirelessaccess to the network by a plurality of client devices. Each of theaccess devices is configured to transmit probes to the client devicesand to receive responses from the client devices corresponding to theprobes. A first one of the access devices is configured to inhibitassociation of the client devices with the first access device wherereceipt of the responses occurs more than a predetermined time periodafter transmission of the corresponding probes, thereby creating a zoneof operation outside of which the client devices are unlikely toassociate with the first access device.

According to yet another specific embodiment, a wireless network isprovided which includes a plurality of access devices for enablingwireless access to the network by a plurality of client devices. Each ofthe access devices is configured to transmit probes to the clientdevices and to receive responses from the client devices correspondingto the probes. A first one of the access devices is configured todetermine distances from the first access device to the client deviceswith reference to time periods associated with the probes and thecorresponding responses. According to one such embodiment, the firstaccess device is further configured to inhibit association of selectedones of the client devices with the first access device where thedistances associated with the selected client devices are greater than apredetermined distance, thereby creating a zone of operation outside ofwhich the client devices are unlikely to associate with the first accessdevice.

According to another such embodiment, a first one of the distances isfrom the first access device to a first one of the client devices.Second and third ones of the access devices are configured to determinesecond and third distances from the second and third access devices,respectively, to the first client device. A first process operating inthe network is operable to determine a position of the first clientdevice with reference to the first, second, and third distances.According to an even more specific embodiment, the first process isfurther operable to facilitate association of the first client devicewith one of the access devices with reference to the position of thefirst client device.

According to a still further embodiment, a wireless network is providedwhich includes a plurality of access points for enabling wireless accessto the network by a plurality of client devices. A first one of theaccess points is configured to facilitate association of the clientdevices with the first access point by broadcasting a first set ofservice set identifiers. The first access point is further configured tofacilitate association of selected ones of the client devices inresponse to transmissions from the selected client devices identifyingadditional service set identifiers not included in the first set ofservice set identifiers.

According to yet a further specific embodiment, a wireless network isprovided which includes a plurality of access devices for enablingwireless access to the network by a plurality of client devices. Firstones of the access devices are configured to transmit signals having afirst polarization. Second ones of the access devices are configured totransmit signals having a second polarization different from the first.The first and second access devices are deployed to mitigate friendlyinterference among the access devices. According to a more specificembodiment, the first and second polarizations are clockwise andcounter-clockwise polarizations. According to another more specificembodiment, deployment of the first and second access devices results ina high-noise environment for the client devices such that each of theclient devices tends to migrate to a nearest one of the first and secondaccess devices.

According to yet a further specific embodiment, a system is disclosedwhich includes a plurality of access points for enabling wireless accessto a network. First ones of the access points are configured to transmitand receive signals having a first polarization, and second ones of theaccess points are configured to transmit and receive signals having asecond polarization different from the first polarization. The accesspoints are configured with a wild card response to facilitateassociation of a client device for any service set identifier requestedin transmissions from the client device. The client device is caused toassociate with one of the access points and gain access to the networkwithout a specific service set identifier requested by the client devicebeing preprogrammed into the access points before the specific serviceset identifier is requested by the client device.

According to yet a further specific embodiment, a method of providing awildcard service set identifier response is disclosed. The method isperformed in a system comprising a plurality of access points enablingwireless access to a network. First ones of the access points areconfigured to transmit and receive signals having a first polarization,and second ones of the access points are configured to transmit andreceive signals having a second polarization different from the firstpolarization. The method includes receiving at one or more of the accesspoints a probe from a client device requesting a specific service setidentifier, and responding to the client device by the one or moreaccess points in order to facilitate wireless association of the clientdevice to one of the one or more access points regardless of thespecific service set identifier requested by the client device. Theclient device is caused to associate with the one of the one or moreaccess points and gain access to the network without a specific serviceset identifier requested by the client device being preprogrammed intothe access points before the specific service set identifier isrequested by the client device.

According to yet a further specific embodiment, a wireless access pointis disclosed including an antenna, a connection port providing wiredcommunications with a network, one or more processors, and a storagedevice having software stored therein. When executed by the one or moreprocessors the software causes the wireless access point to respond to aprobe from a client device requesting a specific service set identifieraccording to a wildcard service set identifier response in order tofacilitate wireless association of the client device with the wirelessaccess point regardless of the specific service set identifier requestedby the client device, and to provide the client device with wirelessaccess to the network. In this way, the client device is enabled toassociate with the wireless access point and receive access to thenetwork without a specific service set identifier requested by theclient device being preprogrammed into the wireless access point beforethe specific service set identifier is requested by the client device.

According to yet a further specific embodiment, an access point isdisclosed including an antenna, one or more processors, and a storagedevice having software instructions stored therein. When executed by theone or more processors the software instructions cause the one or moreprocessors to store a programmable response time for defining a zone ofoperation around the access point, receive from a client device arequest to associate with the access point, transmit a probe to theclient device in response to receiving the request, monitor incomingpackets to determine whether the client device responds to the probe,receive a response to the probe from the client device, measure a roundtrip time between transmission of the probe and receipt of the responseto the probe, determine whether the round trip time is longer than theprogrammable response time, allow the client device to associate withthe access point in response to determining that the round trip time isless than the programmable response time, and deny the request toassociate with the access point in response to determining that theround trip time is longer than the programmable response time.

According to yet a further specific embodiment, a method of managingwireless access to a network is disclosed—the method performed by anaccess point coupled to network. The method comprises: storing aprogrammable response time for defining a zone of operation around theaccess point, receiving from a client device a request to associate withthe access point, transmitting a probe to the client device in responseto receiving the request, monitoring incoming packets to determinewhether the client device responds to the probe, receiving a response tothe probe from the client device, measuring a round trip time betweentransmission of the probe and receipt of the response to the probe,determining whether the round trip time is longer than the programmableresponse time, allowing the client device to associate with the accesspoint in response to determining that the round trip time is less thanthe programmable response time, and denying the request to associatewith the access point in response to determining that the round triptime is longer than the programmable response time.

According to yet a further specific embodiment, a non-transitoryprocessor-readable medium is disclosed. The non-transitory processorreadable medium comprises a plurality of processor-executableinstructions that when executed by one or more processors cause the oneor more processors to perform a plurality of steps including: storing aprogrammable response time for defining a zone of operation around theaccess point, receiving from a client device a request to associate withthe access point, transmitting a probe to the client device in responseto receiving the request, monitoring incoming packets to determinewhether the client device responds to the probe, receiving a response tothe probe from the client device, measuring a round trip time betweentransmission of the probe and receipt of the response to the probe,determining whether the round trip time is longer than the programmableresponse time, allowing the client device to associate with the accesspoint in response to determining that the round trip time is less thanthe programmable response time, and denying the request to associatewith the access point in response to determining that the round triptime is longer than the programmable response time.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified network diagram of an exemplary wireless localarea network in which embodiments of the present invention may beimplemented.

DETAILED DESCRIPTION

Reference will now be made in detail to specific embodiments of theinvention including the best modes contemplated by the inventors forcarrying out the invention. Examples of these specific embodiments areillustrated in the accompanying drawings. While the invention isdescribed in conjunction with these specific embodiments, it will beunderstood that it is not intended to limit the invention to thedescribed embodiments. On the contrary, it is intended to coveralternatives, modifications, and equivalents as may be included withinthe spirit and scope of the invention as defined by the appended claims.In the following description, specific details are set forth in order toprovide a thorough understanding of the present invention. The presentinvention may be practiced without some or all of these specificdetails. In addition, well-known features may not have been described indetail to avoid unnecessarily obscuring the invention.

FIG. 1 is a simplified network diagram of an exemplary wireless localarea network 100 in which embodiments of the present invention may beimplemented. Wireless access points 102 in conjunction with switch 103provide access to network 100 to a variety of client devices. It shouldbe noted at the outset that the equipment and network configurationshown merely represent one example of the wide variety of environmentsin which the invention may be practiced. For example, wireless accesspoints 102 may be implemented according to any of IEEE 802.11b, 802.11g,802.11a, 802.16, etc., and may represent products provided by supplierssuch as, for example, Colubris Networks of Waltham, Mass., or CiscoSystems of San Jose, Calif. Additionally, the connection between accesspoints 102 and the network (as represented by switch 103 which mayitself represent one or more of a wide variety of switches and routers)is represented as wireless, but may be wired. In general, the techniquesdescribed herein are more widely applicable and should not be limited tothe network configurations, standards, or vendors referred to herein.

In addition, the various functionalities described herein may beimplemented in a variety of ways. For example, various aspects of thesefunctionalities may be implemented in hardware, firmware, or softwareassociated with the various devices in a wireless network. These devicesinclude wireless access points or base stations, associated computingdevices (e.g., servers and switches), and, in some cases, the clientdevices operating in the network. The functionalities may be performedor controlled by a single device or may be performed in a distributedmanner by more than one device in the network. Thus, although exemplaryembodiments described herein may refer to particular approaches toimplementing the various functionalities of the invention, those ofskill in the art will understand that these references are not intendedto limit the invention.

It should also be noted that, as used herein, the term “client device”refers to any of a wide variety of devices which operate in a wirelessnetwork including, for example, any type of wireless computing device(e.g., laptops, handheld devices, etc.), any type of wirelesstelecommunications device (e.g., cell phones, messaging clients, etc.),inventory devices (e.g., point-of-sale, bar code scanners, etc.), ordevices performing functions as peripherals to standard or commondigital or analog systems.

According to various embodiments of the invention, techniques areprovided which may be used individually or in various combinations toimplement functionalities typically associated with geographic isolationin complex wireless environments, e.g., providing different levels ofaccess or service in well-defined geographic zones of operation. Incontrast with conventional approaches which attempt to mitigate theeffects of noisy environments, some of the embodiments of the inventionactually take advantage of low signal-to-noise ratios and signaldistortion to achieve these functionalities. For example, according tosome embodiments, signal interference and/or signal distortion may causeclient devices to disassociate from access points or base stations inpredictable and intended ways even in the presence of very high signallevels.

In systems employing IEEE 802.11 or similar wireless technologies, eachsession for packet transfer, including the connection data rate, isnegotiated between the client and the wireless access point. That is,the client and the access point negotiate the data rate on apacket-by-packet basis. Therefore, according to a specific embodiment ofthe invention, restricting the data rate at which a client is allowed toassociate controls the usable sphere of influence or operational zone ofthe access point.

As will be understood, it is difficult for a client to maintain a datarate of 11 Mbps (802.11b) or 54 Mbps (802.11a, 802.11g) connecting to anaccess point through an obstruction; even a window or thin partition. Asthe signal passes through a barrier it is distorted due to reflectionand refraction from the barrier regardless of the strength of thesignal. These effects are further exacerbated by the “noise” associatedwith other nearby access points. Thus, by enforcing a minimum datatransfer rate, when the client leaves a hotel conference room, forexample, it cannot “turn down” the data transfer rate to stay associatedwith the access point in the conference room and so will disconnect asdesired.

According to some embodiments, the ability to enforce a minimum datatransfer rate may be enabled using existing access point features whichprovide control over the data transfer rate. For example, some accesspoints may be configured to set a maximum data rate for QoS purposes,i.e., to keep some devices from starving other devices. Such a featuremay also facilitate compatibility with certain client devices that onlyhandle specific data rates (i.e., as opposed to all the rates specifiedby the standards). As will be understood, this minimum data rate may beadjusted so that the usable area is appropriate for the roomconfiguration or the desired geographic zone size.

An example may be illustrative. A client device 104 may initially beassociated with an access point 102-1 with a strong signal in the publicarea 106 of a hotel. The client 104 then wanders into another area(e.g., a private meeting room 108 with different security, permissions,and access rules) while still associated to the public area access point102-1. Because of the noise and/or distortion caused by the physicalbarriers (even low attenuation barriers) and competing access points(e.g., lost node scenario), the client device 104 breaks its connectionwith the public area access point 102-1 within a few packets (regardlessof its data rate or, to a large margin, link strength) and probes foravailable access points for its service set identifier (SSID). When anaccess point receives the probe, it advertises its availability, andsubsequently the access point and client device initiate the proceduresfor association and authentication.

Due to its closer proximity, the private meeting area access point 102-2(i.e., the access point or one of a group of access points intended forthat private meeting area) is the first to respond (i.e., the near/farscenario). The client then associates to the closer (i.e., the privatemeeting area) access point 102-2 and becomes party to the permissions,restrictions, security, and benefits associated with that geographicoperational zone. Some time later the client device 104 may physicallyleave the area by simply passing through an exit. Then, due to thesignal attenuation and distortions caused by the environment's boundaryconditions (e.g., physical barriers and reflective/multipath conditions)the client 104 is incapable of sustaining the predetermined connectiondata rate (e.g., 11 or 54 Mb under 802.11b and 802.11a/g respectively).And because the private area access point 102-2 is configured to refuseany lower data rates, the client is forced back to the public areaaccess point 102-1.

According to another specific embodiment of the invention, theoperational zone of an access point is controlled with reference to theamount of time required for round trip communications between the accesspoint and associated client devices. Everything between an access pointand a client device involves some form of a handshake. Often this takesthe form of a probe and response, e.g., an acknowledgment (ACK) requestto and an ACK response from the client device and is handled on the PHY(tertiary) level of the device technology. As dictated by the laws ofphysics relating to signal propagation, the round trip time of thesehandshakes, e.g., the time required for an ACK response from the client,represents the distance from the access point. Therefore, according to aspecific embodiment of the invention, where the client is further thansome distance from the access point, e.g., the ACK response takes longerthan some programmable time period, the client is not allowed toassociate (or continue to associate) with the access point.

According to a specific embodiment, the ACK response time of the accesspoint (e.g., 102-3) is manipulated such that client devices (e.g.,device 110) outside of a desired range 114 are unable to respond to anACK from the access point 102-3 within the response time, while clientdevices inside range 114 (e.g., device 116) can. This approach makes itpossible to significantly limit the range of an access point (i.e., theaccess point will not wait long enough for a distant client's responseto reach it), while still providing a high enough RF signal to accountfor shadows or weak spots within the intended coverage area of theaccess point (e.g., meeting room 117).

According to yet another specific embodiment, the operational zone of anaccess point is again defined with reference to the amount of timerequired for round trip communications between the access point andassociated client devices. According to this approach, the response timeis used to determine the distance to the client (as opposed to simplysetting the acceptable response time to prevent associations). Thisdistance is then used to make decisions such as, for example,determining whether or not a connection will be allowed or maintained.In IEEE 802.11 systems, the Logical Link Control (LLC) and Media AccessControl (MAC) layers employ at least five distribution services whichcan be exploited for such information. The simplest is the wait statewhich is controllable and can be monitored at the PHY level. Theadvantage of this approach is that it can be implemented and/ormanipulated at the lowest network level, therefore requiring lessprocessing time. However, any probe and response may be employed forthis purpose.

A numerical example may be illustrative. When a TCP packet istransmitted in an IEEE 802.11 network, the receiving device sends an ACK212.18 μs after receiving the packet. This represents the time requiredby the receiving device to process an 18 byte preamble (144 μs), a 6byte header (48 μs), 14 bytes of ACK data (10.18 μs), and interfacespace (10 μs). If the round trip time as measured by the transmittingdevice is 213.3 μs, this represents a signal propagation time to thereceiver and back of 01.12 μs (1120 ns). Because the distance betweenthe transmitting and receiving devices is the measurement needed, thetravel time is divided by two 1120 ns/2=560 ns. Because radio wavespropagate about 11.8 inches in 1 ns, the distance between the devices isapproximately 560×11.8/12=550.7 feet. An access point may therefore beset, for example, to deny a client access or to terminate a connectionif the client is over 400 feet away (i.e., if round trip time for theprobe/ACK is longer than 212.99 μs after the probe is sent). The clientis then forced to associate with an alternate access point. According tosome implementations, reflections due to barriers will add small traveltime to the wave front and may need to be accounted for.

According to some embodiments, the distances a, b, and c of a client 118from multiple access points (e.g., 102-1, 102-4, and 102-5) may bedetermined. These distances may then be employed (e.g., by an agent(e.g., server 120) in communication with the multiple access points) todetermine a position of the client (as opposed to a linear distance froma particular access point) so that a decision may be made based on theclient's position as to which AP the client should associate with,and/or the types of services to be made available to the client. Thedetermination of position may be done to varying degrees of precisionand may be accomplished, for example, using any of a wide variety oftriangulation algorithms known in the art.

As will be appreciated with reference to the above-describedembodiments, a wireless network may be constructed according to theinvention in which multiple access points or base stations operate inwell-defined geographic zones of operation. However, in some situations,circumstances beyond the control of the network provider may interferewith such carefully configured environments. For example, a networkconfigured in accordance with the invention may be deployed in a hotel,but a wireless hotspot in an adjacent coffee house might flood thecarefully constructed network with its transmissions. Because FCCregulations prohibit the jamming of such signals, it is likely thatdevices associated with hotel guests may request connection to the SSIDassociated with the coffee house access point instead of one of theaccess points in the hotel.

One approach to this problem would be to configure the hotel's accesspoints to respond to a client's response to a probe from the coffeehouse access point. However, current top-of-the-line access points onlyallow specification of limited number of SSIDs. Given that SSIDs arespecified with up to 32 alphanumeric characters, such an approach wouldundesirably force the hotel to use the SSIDs of the adjacent businessesrather than the ones they would like to use. Therefore, according to aspecific embodiment, wireless access points implemented in accordancewith the invention are enabled to accept connections from client deviceseven where the requested SSID is not one of the ones specified for thoseaccess points. This “wild card” response to any SSID probe makes itvirtually impossible for any client device to associate with an accesspoint out of the desired area. That is, the access points within thedesired area will respond to probes from the client devices before theaccess points outside of the desired area, and the client devices willassociate preferentially with the access point that responds first. Thiswill effectively circumvent any attempt to associate with the accesspoint outside of the desired area and will increase the number ofdevices and network traffic for the access points inside the desiredarea. According to more specific embodiments, the foregoing approach maybe employed in combination with one or more geographic area restrictiontechniques to inhibit devices outside of the desired area fromassociating with access points within the desired area.

As mentioned above, the approaches to geographic isolation and clientlocation described herein may be used individually or in variouscombinations to achieve the desired zone of operation and/or relatedfunctionality. For example, it is clear from FIG. 1 that the range 114defined around access point 102-3 extends into the adjacent meeting room108 and the public area 106. That is, the geographic zone defined by thesingle technique relating to device response time defines a sphericalregion around access point 102-3 which extends beyond the intendedcoverage area, i.e., meeting room 117. However, if this technique iscombined with the technique in which a minimum or specific data rate isenforced (e.g., as described above with reference to meeting room 108),this could have the effect of eliminating the portions of the sphericalzone represented by range 114 outside of room 117. That is, becauseclient devices outside of room 117 will not be able to sustain the datarate required by access point 102-3 (e.g., because of the interveningwalls), they will not be able to associate with that access point evenif they are within range 114.

In another example, the technique described above in which the positionof client device 118 is determined may be combined with the responsetime technique to improve the reliability with which the geographicisolation and related functionality may be effected. That is, inaddition to determining which access point with which client 118 shouldassociate, the association would only be allowed if client 118 was ableto respond to the selected access point within the programmed responsetime.

As will be understood, the foregoing combinations are described by wayof example. A variety of other combinations of the described techniquesand their equivalents and variants will be apparent to those of skill inthe art and are therefore included within the scope of the invention.

Due to the limited capacity of and high demands placed on wirelessaccess points, it is often necessary to provide additional access pointsin some applications in order to better serve the volume of clientdevices. However, a problem arises relating to interference between andamong closely spaced access points (often referred to as “friendly”system noise). This interference can result in protection mechanisms(e.g., clear to send/clear to receive cycles, or carrier sense multipleaccess) being enabled which, in turn, cause the network to slow down. Inaddition, such interference can compromise data integrity, causingpacket retries and thereby further reducing system performance.

As mentioned above, current practice is to select different channels forclosely spaced access points to minimize interference (e.g., use ofchannels 1, 6, and 11 in the 802.11b/g band are often recommended bymanufacturers for this purpose because they do not overlap). However,such an approach is not adequate for the access point densities requiredin some applications. Therefore, according to various embodiments of thepresent invention, the number and/or density of access points isincreased by the reduction of friendly system noise to the access pointswhile allowing a high level of friendly system to the clients throughthe use of mixed polarizations.

Transmitted radio signals reflect off objects creating a conditioncalled “multi-path” in which a signal follows several paths to thereceiver. On long point-to-point radio links stratification of theatmosphere can create multiple paths by refracting the signal. Becauseof their longer path lengths, these reflected or refracted signals takelonger to arrive at the receiver where they can interfere with the mainsignal. It is common for wireless systems to combine polarizationdiversity with spatial diversity to take advantage of the multi-pathcondition. This requires the installation of two antennas separatedvertically or horizontally. Vertical separation works well for longerfree-space line-of-sight links, while horizontal separation works bestfor partially obstructed or non-line-of-sight links. The signalsreceived by both antennas are combined to enhance the quality of thesignal where multi-path exists. Mixed polarization has been a commonpractice since the 1940s and has been used as a form of diversity inorder to clear up signals, or in some cases to co-locate like systems ona single structure for point-to-point applications or for radar.

According to specific embodiments of the invention, adjacent or closelyspaced access points or base stations in a wireless network areconfigured with different polarizations to enable denser placement ofthese devices and to thereby increase the capacity of the system.According to a specific embodiment, opposing circular polarizations(e.g., clockwise and counter-clockwise) are employed. In such animplementation, transmissions from an antenna with a clockwisepolarization have a theoretical rejection ratio approaching 29 dB (and apractical rejection ratio of 20 dB) when received by an antenna using acounter-clockwise polarization. Embodiments of the invention takeadvantage of this rejection ratio to reduce the likelihood of friendlyinterference at the access point, thus increasing the number of accesspoints that can be deployed in a given environment.

As mentioned above, client devices make the decision to handoff from oneaccess point to another based on the signal-to-noise ratio theyexperience, thus allowing them to select the most appropriate accesspoint in a cluttered environment. As such, a reduction of noise asexperienced by the client device in such an environment is undesirable.Fortunately, the mixed polarization approach of the present inventiondoes not reduce the noise at the client. In some cases, such embodimentsresult in a high noise environment for the client devices which, inturn, advantageously causes the client devices to migrate to closer orless populated access points or base stations.

While the invention has been particularly shown and described withreference to specific embodiments thereof, it will be understood bythose skilled in the art that changes in the form and details of thedisclosed embodiments may be made without departing from the spirit orscope of the invention. For example, the mixed polarization techniquedescribed above could be combined with any of the geographic isolationand client location techniques described herein to implement a wirelessnetwork with high capacity and well-defined zones of operation.

And despite references to a hotel environment, it will be understoodthat the techniques described herein may be applied in a wide variety ofwireless network environments. For example, wireless networks inmanufacturing and warehouse facilities could be improved using any ofthe techniques described herein. In addition, the various techniques ofthe present invention may be applied to wireless networks implementedwith technologies outside of the IEEE 802.11 family of standards, e.g.,wireless telecommunications networks.

Finally, although various advantages, aspects, and objects of thepresent invention have been discussed herein with reference to variousembodiments, it will be understood that the scope of the inventionshould not be limited by reference to such advantages, aspects, andobjects. Rather, the scope of the invention should be determined withreference to the appended claims.

What is claimed is:
 1. A method of managing wireless access to anetwork, the method performed by an access point coupled to the network,the method comprising: storing a programmable response time for defininga zone of operation around the access point; receiving from a clientdevice a request to associate with the access point, wherein the requestto associate is an attempt by the client device to establish a linkbetween the access point and the client device according to an IEEE802.11 protocol; transmitting a probe to the client device in responseto receiving the request; monitoring incoming packets to determinewhether the client device responds to the probe; when a response to theprobe is received from the client device, measuring a round trip timebetween transmission of the probe and receipt of the response to theprobe; determining whether the round trip time is longer than theprogrammable response time; allowing the client device to associate withthe access point in response to determining that the round trip time isless than the programmable response time; denying the request toassociate with the access point in response to determining that theround trip time is longer than the programmable response time; andtransmitting data between the client device and the network via theaccess point only while the client device is associated with the accesspoint.
 2. The method of claim 1, wherein the probe is an acknowledgement(ACK) request and the response is an ACK response.
 3. The method ofclaim 2, further comprising sending the probe and detecting the responseto the probe at a physical network layer of the access point.
 4. Themethod of claim 1, further comprising transmitting a second probe to theclient device after allowing the client device to associate with theaccess point; receiving from the client device a response to the secondprobe; measuring a second round trip time between transmission of thesecond probe and receipt of the response to the second probe;determining whether the second round trip time is longer than theprogrammable response time; allowing the client device to continue toassociate with the access point in response to determining that thesecond round trip time is less than the programmable response time; notallowing the client device to continue to associate with the accesspoint in response to determining that the second round trip time islonger than the programmable response time.
 5. The method of claim 1,further comprising manipulating the programmable response time accordingto a desired geographical zone of operation around the access point. 6.The method of claim 5, further comprising calculating the programmableresponse time according to a predetermined distance representing thedesired geographical zone of operation around the access point, around-trip signal propagation time given the predetermined distance, anda processing time of the client device given a packet size of the probeas transmitted by the access point.
 7. The method of claim 1, wherein,when no response to the probe is received from the client device withinthe programmable response time, denying the request to associate withthe access point.
 8. The method of claim 1, further comprisingconverting the round trip time into a distance between the client deviceand the access point by taking into account a processing time of theclient device given a packet size of the probe as transmitted by theaccess point.
 9. The method of claim 8, further comprising sending thedistance to an agent on the network.
 10. A non-transitoryprocessor-readable medium comprising a plurality of processor-executableinstructions that when executed by one or more processors cause the oneor more processors to perform steps of: storing a programmable responsetime for defining a zone of operation around an access point; receivingfrom a client device a request to associate with the access point,wherein the request to associate is an attempt by the client device toestablish a link between the access point and the client deviceaccording to an IEEE 802.11 protocol; transmitting a probe to the clientdevice in response to receiving the request; monitoring incoming packetsto determine whether the client device responds to the probe; when aresponse to the probe is received from the client device, measuring around trip time between transmission of the probe and receipt of theresponse to the probe; determining whether the round trip time is longerthan the programmable response time; allowing the client device toassociate with the access point in response to determining that theround trip time is less than the programmable response time; denying therequest to associate with the access point in response to determiningthat the round trip time is longer than the programmable response time;and transmitting data between the client device and a network via theaccess point only while the client device is associated with the accesspoint.
 11. An access point for managing wireless access to a network,the access point comprising: an antenna; one or more processors; and astorage device having a plurality of software instructions storedtherein that when executed by the one or more processors cause the oneor more processors to: store a programmable response time for defining azone of operation around the access point; receive from a client devicea request to associate with the access point, wherein the request toassociate is an attempt by the client device to establish a link betweenthe access point and the client device according to an IEEE 802.11protocol; transmit a probe to the client device in response to receivingthe request; monitor incoming packets to determine whether the clientdevice responds to the probe; receive a response to the probe from theclient device; measure a round trip time between transmission of theprobe and receipt of the response to the probe; determine whether theround trip time is longer than the programmable response time; allow theclient device to associate with the access point in response todetermining that the round trip time is less than the programmableresponse time; deny the request to associate with the access point inresponse to determining that the round trip time is longer than theprogrammable response time; and transmit data between the client deviceand the network only while the client device is associated with theaccess point.
 12. The access point of claim 11, wherein the probe is anacknowledgement (ACK) request and the response is an ACK response. 13.The access point of claim 11, wherein sending the probe and detectingthe response to the probe is performed at a physical network layer ofthe access point.
 14. The access point of claim 11, wherein, byexecuting the software instructions, the one or more processors arefurther configured to: transmit a second probe to the client deviceafter allowing the client device to associate with the access point;receive from the client device a response to the second probe; measure asecond round trip time between transmission of the second probe andreceipt of the response to the second probe; determine whether thesecond round trip time is longer than the programmable response time;allow the client device to continue to associate with the access pointin response to determining that the second round trip time is less thanthe programmable response time; not allow the client device to continueto associate with the access point in response to determining that thesecond round trip time is longer than the programmable response time.15. The access point of claim 11, wherein, by executing the softwareinstructions, the one or more processors are further configured tomanipulate the programmable response time according to a desiredgeographical zone of operation around the access point.
 16. The accesspoint of claim 15, wherein, by executing the software instructions, theone or more processors are further configured to calculate theprogrammable response time according to a predetermined distancerepresenting the desired geographical zone of operation around theaccess point, a round-trip signal propagation time given thepredetermined distance, and a processing time of the client device givena packet size of the probe as transmitted by the access point.
 17. Theaccess point of claim 11, wherein, when no response to the probe isreceived from the client device within the programmable response time,the one or more processors are configured to deny the request toassociate with the access point.
 18. The access point of claim 11,wherein, by executing the software instructions, the one or moreprocessors are further configured to convert the round trip time into adistance between the client device and the access point by taking intoaccount a processing time of the client device given a packet size ofthe probe as transmitted by the access point.
 19. The access point ofclaim 18, wherein, by executing the software instructions, the one ormore processors are further configured to send the distance to an agenton the network.
 20. A system comprising a plurality of access pointseach as set forth in the access point of claim 11, wherein at least twoof the access points have different programmable response times.